It is the practice to feed gobs of molten glass to glass forming machine sections at a rate of 10 to 20 gobs per minute for each mold cavity, depending upon the weight of the gob. These gobs are formed by the shearing of a stream of glass issuing from the bottom of a forehearth. The shearing mechanism used in these operations has been the scissor type which swings generally about a pivot point adjacent one side of the end of the feeder, or what is more commonly termed "feeder bowl". The two blade carrying arms operate much as the blades of a scissors, to bring the two shear blades into overlapping relationship on the axis of the stream of glass. With the advent of more productive machines, which will handle four or more gobs of glass simultaneously, there has become a necessity for feeder mechanisms which can consistently shear four or more streams of glass into gobs simultaneously at a controlled repetitive rate. Feeding the higher productivity glass forming machine, and in particular glass bottle forming machines having quadruple cavities per section and as many as 10 side-by-side sections, has become a reality.
By way of background, several recent patents have issued on straight line glass stream cutting apparatus. One U.S. Patent is U.S. Pat. No. 3,592,938, issued July 13, 1971 to R. S. Bracket et al. In this patent, the two shear blade holders are moved toward and away from each other by an interconnecting rack and pinion arrangement with a drive lever or link coming from the normal rotating shear drive cam which oscillates a lever, which in turn is coupled to one of the shear arm holders. This shear arm holder carries a rack which drives through a pinion to a second rack carried by an opposite or opposing shear blade holder, and oscillation of the drive rod will cause the shear blades to move toward and away from each other along essentially a straight line, since both blade holders are mounted for movement along horizontal rods positioned at one side of the area of the feeder bowl axis.
A second U.S. Pat. No. 4,174,647, issued Nov. 20, 1979 in the name of Dahms, and the several divisions thereof, also disclose a straight line shear mechanism. In this particular patent, there is shown in FIG. 1 a shear mechanism comprising a generally horizontal frame, which includes end plates that are interconnected by side rails. The side rails, along with supporting rods for the shear blade holders, constitute a rectangular frame which surrounds the axis of the streams of molten glass that would issue from the feeder. This frame is mounted to a post which, as stated in the patent, is mounted to a feeder bowl by any suitable means. The particular shear mechanism described in this patent is air operated in that it has an air motor which is used to provide the driving force for the shear blades as they reciprocate toward and away from each other while guided by the side rails. In addition, this patent shows drop guides which are adjustable relative to their mounting and the blade carrying mechanism.
In addition to the foregoing patent, a copending application, Ser. No. 398,122, filed July 14, 1982, now U.S. Pat. No. 4,450,741 of common assignee, discloses a straight line glass shearing apparatus which has some similarities to the present invention. The above-noted copending application provides a straight line gob shearing mechanism with drop guides that travel with the shears and engage adjustable stops. The adjustment of the drop guide stops may be made while the mechanism is in operation. In addition, the tension on the blades may be adjusted with respect to any individual pair when the mechanism is out of operation. Furthermore, the height of the shears, and therefore the horizontal shearing plane, can be adjusted by the fact that the entire shearing mechanism is mounted to the feeder bowl by a vertically adjustable post.
With the foregoing in mind, it is an object of this invention to provide apparatus which will move the shear blades into and out of engagement with the stream of glass to form gobs wherein the shear blades move in straight paths, relative to each other, both toward and away from each other. By providing the parallel operating shear arm mechanism, it is believed that a superior and better control of the shear operation can be obtained. One of the drawbacks with respect to the shearing of multiple gobs with arms which operate, in effect from adjacent pivot axes at one side or the other of the feeder bowl, is that the multiple shear blades are moving through plural arcs rather than moving in a straight path across the stream of glass. With the shears moving through different arcs, it is even more difficult sometimes to accurately control the degree of overlap of the shears, and by reason of the outer shears moving at a slightly greater velocity than the shears more closely positioned relative to the pivot points, there is a tendency for the shear mechamism to inconsistently cut all of the multiple gobs at the same weight. To be able to provide the gobs to the forming machine, such that they are all of the same and consistently equal weights through an extended period of plural gob feeding, is a major goal of the present invention.
An additional object of the present invention is to provide a mechanism in which the shear blade mounting mechanism is supported such that it may be swung away from the area of the feeder for repairs or to provide access to the bottom of the feeder without disturbing the linkage to the shear drive cam.
It is a further object of the present invention to provide a mechanism which is movable out of the shear area without interfering with or requiring the specific interruption of the glass streams, if desired.
It is an additional object of this invention to provide a drop guide mechanism which moves with the upper shear blades and to provide a mechanism for adjusting the position of the drop guide to a precise location while in operation and without the requirement of a complicated mechanical system which would be subject to excessive wear.
It is a still further object of the present invention to provide a glass gob shearing mechanism which will simultaneously cut four gobs at a single stroke, with the lower set of shear blades being vertically adjustable, as a unit, to permit adjustment of shear tension while the mechanism is in operation.